You can get screenprinting supplies at most art stores like Opus, Loomis. Check out the Speedball stuff. Its not the dopest stuff but if you want to do it yourself then its an option.
You can even get some places to burn a screen for you, check out Wilcox on Marine.
If you are going to do over 20 units of the graphic and more than one colour then I would go to the pros. There are tons in this city to pick from (design, orion, impressions, Griffin House, Tinelle and tons more). Go check out some samples and some prices.